This invention relates to an analogue interface for a self-contained information exchange circuit.
Self-contained information exchange circuits can be used on objects, for example such as objects processed on a production line, or portable data storage cards. Information exchanges between the self-contained information exchange circuit and a fixed station take place inductively without any contact.
The information exchange circuit, and the object on which it is used, are usually not provided with an independent electrical power supply. The energy necessary for their operation is supplied inductively from the fixed station.
Consequently, the analogue interface according to the invention performs a data transmission/reception function and a function to supply electrical power to the circuit on which it is used.
The invention is used in applications, particularly for the identification and sorting of objects to be made, processed or stored, and in portable xe2x80x9csmart cardxe2x80x9d type equipment.
Other examples of uses of the invention are in transport, production monitoring and animal identification activities.
FIG. 1 attached represents the main components of an information exchange circuit used on a portable object and associated with a fixed station, in the form of functional blocks.
The fixed station, marked with general reference 10, is provided with an antenna 12 capable of receiving a signal from an information exchange circuit used on a mobile object and capable of transmitting a signal to this circuit.
The information exchange takes place by modulation of a carrier wave.
The general reference 20 indicates an information exchange circuit used on a mobile object not shown. This circuit is also provided with an antenna 22 for transmission and reception of a carrier wave that may be modulated by the exchange circuit 20 (in transmission mode) or by the fixed station 10 (in reception mode).
An analogue interface 24 for the circuit 20 has an input/output 23 connected to antenna 22 and a first input/output 25 for exchange of data signals with a logical processing unit 26 such as a microprocessor unit. The logical unit is associated with memory means 28 in which data to be exchanged are stored.
A second output 30 from the analogue interface outputs an electrical power supply energy to the logical unit 26 and the memory 28, as shown by an arrow 31. This energy is output from the inductive energy received by the antenna 22.
The document (1) referenced at the end of this description describes an analogue interface for an information exchange circuit adapted to xe2x80x9cOn/Offxe2x80x9d type modulation on reception. The interface comprises two rectification and regulation units designed to extract data, information and the power supply energy necessary for the circuit, from the signal present at the terminals of an antenna.
This type of interface operates satisfactorily within a given amplitude range of the received signal. When the received signal is weak, the information exchange circuit no longer works due to an insufficient electrical power supply.
Conversely, when the field applied to the antenna is very strong, very high currents pass through the rectification and regulation units. Thus, the components of these units need to be very much oversized to prevent these units from being destroyed under the effect of overcurrents. However, this constraint is hardly compatible with miniaturization of the information exchange circuit.
Document (2), also referenced at the end of the description, describes an analogue interface for an information exchange circuit based on phase modulation of a carrier wave.
The described device is equipped with means for adjusting the level of the received signal and can overcome difficulties related to overvoltages or overcurrents in interface components.
Operation of this type of device is satisfactory when the frequency of the signal carrier wave (phase modulated) is low, less than 1 MHz. The solution proposed in document (2) for use with a carrier wave frequency greater than 10 MHz, results in unacceptable electricity consumption particularly for demodulation, and hardly compatible with the self-contained nature of information exchange circuits.
The purpose of this invention is to propose an analogue interface for an information exchange circuit that does not have the limitations of the devices mentioned above.
One purpose in particular is to propose this type of interface for an information exchange circuit by amplitude modulation of a carrier wave.
Another purpose is to propose such an interface adapted to operate within a high frequency range with carrier waves at a frequency greater than 10 MHz.
Another purpose is to propose an interface with a very low energy consumption that can be very highly integrated in the form of a chip.
Another purpose is to propose such an interface with a small number of components and adapted for large-scale industrial manufacturing.
Finally, another purpose is to propose an interface capable of operating satisfactorily despite high variations in the intensity of the inductive field received by the antenna in the information exchange circuit.
More precisely, the purpose of the invention to achieve these objectives is an analogue interface for an information exchange circuit by amplitude modulation of a carrier wave, including an interface input designed to be connected to the terminals of an antenna, a demodulator with an output connected to a logical unit in the information exchange circuit, and means of supplying a power supply voltage to the information exchange circuit.
According to the invention, the interface also comprises means of rectifying and filtering the carrier wave connected firstly to an input of the demodulator and secondly to a device for regulating the said power supply voltage.
Due to the characteristics described above, and particularly the regulation device, the circuit may be protected against overcurrents and overvoltages. The only current that passes through the interface and logical unit components is a minimum current necessary for their operation, and the components can be made very small. Furthermore, rectifying and filtering means are used in common for processing the signal intended for the demodulator and for regulation of the power supply. Savings in space, cost, operating energy and manufacturing price can thus be obtained.
Furthermore, the interface may operate at carrier wave frequencies greater than 10 MHz. Rectification and filter means placed immediately behind the antenna can be used to supply a low frequency signal to the demodulator, and therefore to the modular circuit. Signal processing is then possible without causing excessive energy consumption.
The regulation device may comprise means of modifying the antenna impedance as a function of a rectified voltage output by rectification and filter means.
These impedance modification means help to make the antenna more or less receptive to the received inductive field and consequently eliminate current or voltage variations in the circuit that could be caused by variations in the intensity of the inductive field.
According to one particular embodiment of the means of modifying the antenna impedance, these means may comprise a controllable load connected to the input to the interface in parallel to the antenna terminals.
The controllable load may be made for example starting from a field effect transistor in which the channel terminals (source and drain) are connected to the antenna terminals through resistances.
The power supply voltage regulation device may also comprise:
a reference voltage source, and
means of comparing the rectified voltage output by the rectification and filter means, with the reference voltage. The comparison means are connected to a control input applied to means of modifying the antenna impedance to control the impedance modification means as a function of a difference in voltage between the rectified voltage and the reference voltage.
The rectification and filter means may be connected to the demodulator, also through comparison means, and/or can be connected through a direct electrical link.
For example, the comparison means may comprise an amplifier with a positive input connected to the rectifier, a negative input connected to the reference voltage source and a control output connected to the impedance modification means.
The comparison means amplifier may be an operational amplifier in which the non-inverting and inverting inputs form the positive and negative inputs respectively.
The comparison means may also be made from a field effect transistor, particularly a PMOS type transistor, with a grid forming the negative input, a first channel terminal forming the positive input and a second channel terminal forming the output.
Other characteristics and advantages of this invention will become clear after reading the following description with reference to the figures in the attached drawings. This description is given for illustrative purposes only, and is in no way limitative.